This invention relates to telephony and in particular relates to a fault isolation device for determining whether a fault occurring in a telephone system lies with the local telephone company or in customer-owned telephone equipment.
Owing to FCC rulings favorable to purveyors of telephone equipment and also to the influx of competition among manufacturers of communications equipment, more and more telephone customers now furnish their own "customer-owned" equipment, such as private branch exchanges (PPX's) and key systems (KSU's). Formerly, equipment had only been leased from the local telephone company. However, customer-owned equipment is still connected to the local telephone company's dial central office over leased telephone trunks.
When trouble occurs within the telephone system including leased telephone trunks and customer-owned equipment such trouble does not necessarily lie with the telephone company, as it is possible that the phone trouble could exist in the customer-owned equipment. While the telephone company will test and repair its own leased equipment, it has no responsibility for the customer-owned equipment, and if the phone company is called and it is determined that the trouble lies in the customer-owned equipment, the customer will be charged for the service call, notwithstanding that an estimated 80% of such troubles are in the phone company's leased trunks or in the dial central office. The charge for such a service call can amount to as much as $45.00.
In order to avoid such a charge for an unnecessary service call, it is desirable for the customer to determine whether the fault lies with the customer-owned equipment or with the telephone company so that it can be decided whether to call the telephone company or to call in a serviceman for the customer-owned equipment to clear the trouble.
However, in conventional customer-owned PBX and KSU systems, there is no provision for isolating the telephone company trunks from the customer-owned equipment, and thus, there is no easy way that the customer can determine whether the problem lies in his equipment or with the phone company.